Nowadays, one mainstream display mode of organic light-emitting diode display (OLED) device is oxide TFT (oxide thin film transistor) plus WOLED (white OLED) plus COA (color filter on array, i.e., the color filter film is formed on the array substrate). In order to solve the problem of threshold voltage (Vth) drift and luminance nonuniformity, a 3T1C external compensation technology is usually applied in the above mainstream display mode for driving pixels, and here the phrase “3T1C” means a pixel unit comprises three thin film transistors (TFT) and one storage capacitor Cst.